fix: Long-lasting TTID/TTFD spans

[philipphofmann]

📜 Description

Presenting a UIViewController when going to the background could lead to long-lasting TTID/TTFD spans. This is fixed now by not creating TTID/TTFD spans when the FramesTracker isn't running.

Docs PR: getsentry/sentry-docs#10960.

💡 Motivation and Context

A customer reported to get long lasting TTID/TTFD spans for UIViewControllers presented when the didEnterBackgroundNotification is posted. They do this due to privacy reasons.

💚 How did you test it?

Added a small sample to present an UIViewController when the didEnterBackgroundNotification is posted and could sometimes reproduce the problem. This PR fixes that problem. I didn't add the sample as a UITest, because it isn't reliable and this PR addresses an edge case. Furthermore, I added unit tests.

📝 Checklist

You have to check all boxes before merging:

• I reviewed the submitted code.
• I added tests to verify the changes.
• No new PII added or SDK only sends newly added PII if sendDefaultPII is enabled.
• I updated the docs if needed.
• Review from the native team if needed.
• No breaking change or entry added to the changelog.
• No breaking change for hybrid SDKs or communicated to hybrid SDKs.

🔮 Next steps

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.421%. Comparing base (cc31630) to head (cfc1e09).
Report is 1 commits behind head on main.

Additional details and impacted files

@@              Coverage Diff              @@
##              main     #4225       +/-   ##
=============================================
- Coverage   91.429%   91.421%   -0.008%     
=============================================
  Files          611       611               
  Lines        49088     49125       +37     
  Branches     17726     17743       +17     
=============================================
+ Hits         44881     44911       +30     
- Misses        4114      4121        +7     
  Partials        93        93               

Files	Coverage Δ
Sources/Sentry/SentryTimeToDisplayTracker.m	100.000% <100.000%> (ø)
.../Sentry/SentryUIViewControllerPerformanceTracker.m	99.033% <100.000%> (+0.009%)	⬆️
...iewController/SentryTimeToDisplayTrackerTest.swift	100.000% <100.000%> (ø)
...entryUIViewControllerPerformanceTrackerTests.swift	97.977% <100.000%> (+0.095%)	⬆️

... and 4 files with indirect coverage changes

---

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[github-actions]

Performance metrics 🚀

	Plain	With Sentry	Diff
Startup time	1233.54 ms	1253.06 ms	19.52 ms
Size	21.58 KiB	694.62 KiB	673.04 KiB

Baseline results on branch: main

Startup times

Revision	Plain	With Sentry	Diff
f25febb	1238.80 ms	1245.35 ms	6.56 ms
e324230	1252.69 ms	1274.56 ms	21.87 ms
0001a09	1223.90 ms	1249.56 ms	25.66 ms
8cd6cfa	1229.88 ms	1251.45 ms	21.57 ms
25e65a5	1249.08 ms	1277.78 ms	28.70 ms
7cd187e	1243.56 ms	1250.20 ms	6.64 ms
3297d6e	1228.57 ms	1255.04 ms	26.47 ms
3d3a411	1233.37 ms	1246.44 ms	13.07 ms
4af7581	1214.55 ms	1237.10 ms	22.55 ms
0589699	1230.14 ms	1245.18 ms	15.04 ms

App size

Revision	Plain	With Sentry	Diff
f25febb	21.58 KiB	414.92 KiB	393.34 KiB
e324230	22.85 KiB	408.87 KiB	386.02 KiB
0001a09	20.76 KiB	433.19 KiB	412.43 KiB
8cd6cfa	21.58 KiB	571.85 KiB	550.26 KiB
25e65a5	22.85 KiB	403.19 KiB	380.34 KiB
7cd187e	20.76 KiB	401.65 KiB	380.89 KiB
3297d6e	21.58 KiB	418.45 KiB	396.86 KiB
3d3a411	21.58 KiB	418.58 KiB	396.99 KiB
4af7581	22.84 KiB	401.62 KiB	378.77 KiB
0589699	21.58 KiB	656.60 KiB	635.02 KiB

[brustolin]

Pretty straight forward. I believe this will fix the issue.

Just one suggestion but all looks good.